Kamstrup MULTICAL 402, Техническое описание, Страница: 59 / 113

MULTICAL® 402
Kamstrup A/S · Technical Description · 5512-742_M1_GB_01.2016
59
8 Flow Sensor
8.1 Ultrasound combined with piezo ceramics
Through the latest 20 years ultrasonic measurement has proved the most long-term stable measuring principle for
heat measurement. Both experience from ultrasonic meters in operation and repeated reliability tests carried out
in Kamstrup’s accredited long-term test equipment as well as by AGFW in Germany have documented the long-
term stability of ultrasonic meters.
8.2 Principles
The thickness of a piezo ceramic element changes when exposed to an electric field (voltage). When the element
is influenced mechanically, a corresponding electric charge is generated. Therefore, the piezo ceramic element
can function as both sender and receiver.
Within ultrasonic flow measuring there are two main principles: the transit time method and the Doppler method.
The Doppler method is based on the frequency change which occurs when sound is reflected by a moving
particle. This is very similar to the effect you experience when a car drives by. The sound (the frequency)
decreases when the car passes by.
8.3 Transit time method
The transit time method used in MULTICAL
®
The transit time difference of a flow sensor is very small (nanoseconds). Therefore, the time difference is
measured as a phase difference between the two 1 MHz sound signals in order to obtain the necessary accuracy.
402 utilizes the fact that it takes an ultrasonic signal sent in the
opposite direction of the flow longer to travel from sender to receiver than a signal sent in the same direction as
the flow.
Diagram 4
S
IG
N
AL
t
PHASE DIFFERENCE
T
Against flow
With flow